The main safeguard is rule of law. There's a whitelist of information that is allowed to be classified -- spelled out in http://en.wikisource.org/wiki/Executive_Order_13526 .
Information shall not be considered for classification
unless its unauthorized disclosure could reasonably be
expected to cause identifiable or describable damage to
the national security in accordance with section 1.2 of
this order, and it pertains to one or more of the
following:
(a) military plans, weapons systems, or operations;
(b) foreign government information;
(c) intelligence activities (including covert
action), intelligence sources or methods, or
cryptology;
(d) foreign relations or foreign activities of the
United States, including confidential sources;
(e) scientific, technological, or economic matters
relating to the national security;
(f) United States Government programs for
safeguarding nuclear materials or facilities;
(g) vulnerabilities or capabilities of systems,
installations, infrastructures, projects,
plans, or protection services relating to the
national security; or
(h) the development, production, or use of weapons
of mass destruction.
Between rule of law, a law that outlines which categories of things the government is allowed to keep secret, and the fact that even really secret programs of any significant size have to ultimately be staffed with lots of normal citizens, I think it's actually a pretty safe and sane system.
A lot of, if not most of, the current tension in the Middle East dates back to just after WWII, when someone decided it would be a good idea to stick all the people that no one wanted (but wouldn't come right out and say it) in the middle of a bunch of people who were ill-prepared to absorb them (and didn't particularly want them, either).
That pretty much paved the road to our current little slice of Middle Eastern hell.
Much more substantial were the efforts of the US government to overthrow moderate regimes for hardlines who would support them, as well the UK's efforts to deliberately screw up the decolonization efforts by drawing up national boundaries with no regards to the inhabitants' will.
It's complex, but it's ridiculously easy to see where things were wrong, and you don't need the hindsight either.
Take any news report about the middle east and replace the names with cananites, babylonians, persions, egyptians, romans, etc - the story doesn't change.
In fact if you read any books by Josephus - it sounds just like CNN (except better written)
I think the existence of an 'administration' and an 'electorate' pretty much guarantees that they are doing something evil behind your back.
What if the current administration is doing evil something behind the back of the electorate? How would we know about it?
You see, secrecy is a catch-22 proposition. If you're trying to do actual real work of tracking down terrorists, you don't want the whole world to know(at least until years later). But if you're doing something EVIL behind our back, the world have the right to know.
The cablegate? Hardly any reason to get angry over. It make the government looks good. But politicians are overreacting.